The gelation of agarose

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Abstract
The formation and dispersal reactions of elastic, turbid agarose gels in water are interpreted in terms of homogeneously nucleated crystalline junction zones in the form of fibrillar fringed micelles interconnected by polymer strands. The gel junctions melt at ca. 92 °C, whereas the gelation temperature (28–36 °C) depends on the cube root of the agarose concentration. Photon correlation spectra of the sol phase are related to the motion of adventitious impure crystalline calcium sulphate particles some 900 Å across. These particles are coated with adsorbed agarose, giving a hydrodynamic radius of order 0.4 µm, and form dimers in concentrated solutions (0.1 < c < 2.5 wt % agarose) in which case the first cumulant of the field correlation function is proportional to the cube of the scattering vector. Further aggregation leads to the formation of weak viscoelastic gels a few degrees above the normal gelation temperature. In dilute solutions (c < 0.1 wt % agarose) the coated particles diffuse individually, the hydrodynamic radius falling steadily with reduction in temperature until the θ-point is reached, when they form clusters, but do not gel. Added KI, KI3 and KNCS inhibit cluster formation and gelation: (NH4)2SO4 precipitates the agarose.

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